Thursday, 29 July 2010

"YO DAWG" is an internet meme. You can search for the term "YO DAWG" to see many examples. They mostly have this in common: A picture of something inside something similar, lets call this object a, accompanied by the text

"YO DAWG I HERD YOU LIKE TO verb(a) SO WE PUT A a IN YO a SO YOU CAN verb(a) WHILE YOU verb(a)"

Another cliché in terms of photography, is to take a picture of something while holding a lens between the subject and the camera, so that the subject is seen through a lens. The obvious thing to do, is of course to combine these two by letting a be a lens.

First, let's take the image. In the setup below, I used a Panasonic Lumix GH1 camera, with the Lumix Leica 45mm macro lens attached. I used a TTL flash angeled upwards to bounce the light off the white ceiling. I used f/8 to get a reasonable depth of field.

In the front of the camera, I am holding a Nikkor 50mm f/1.8 AIS pancake lens. Virtually any fast normal lens could have been used here. In the background is a Nikkor 24mm f/2 AIS lens.

Due to the CDAF system, I can use autofocus on the camera to make sure the lens on the table is in focus, even when looking at the lens through the 50mm pancake lens. This would have been difficult with PDAF systems on DSLR cameras.

The resulting image looks like this. The lens held could have been more in focus. Had I used an even smaller aperture than f/8, the depth of field would have been better. But I think it is sufficiently in focus.

Looking at a closer crop of the centre of the image, we can see that the lens on the table is in perfect focus, thanks to the CDAF system:

Sunday, 25 July 2010

The Big Mac index is a well known price index. By comparing the price of the Big Mac, available in virtually any country, you get a view of the general cost level in that country.

I've tried to do the same with the Panasonic Lumix 20mm f/1.7 Pancake lens, although I must say the index is far from complete, with only a few number of countries included. I chose a lens, rather than a camera body, since cameras become obsolete, and go on clearance sale after some time. This lens is still pretty new and popular, and is less likely to be subject for various rebates.

Country

Price in local currency

Price in EUR

US

371.95

287.86

Canada

419

312.77

France

332.89

332.89

UK

278.99

332.99

Germany

362.99

362.99

Denmark

2989

401.08

Australia

584

405.06

Sweden

3865

409.72

Norway

3999

501.41

The conclusion is not surprising: It's best to be a consumer in a big market.

Friday, 23 July 2010

I have an old legacy tele lens, the Nikkor 200mm f/4 AIS. It is well suited for use on a Micro Four Thirds camera, since both the focus and aperture are operated manually by twisting the rings on the lens. This is in contrast to Canon EF lenses, in which the aperture is operated electronically, and no adapter is available to control this from a Micro Four Thirds camera.

This is a compact and high quality tele lens. The moderate maximum aperture, f/4, makes it less bulky than professional f/2.8 lenses. However, it still gives good quality images already from f/4.

The construction is fairly simple with five lenses in five groups. This is a mature lens design, and gives a good performance overall. It has nine aperture diaphragm blades.

The lens is made of metal, and the focus ring has a well dampened professional feel. The aperture ring can be set at any size, but has click stops at one unit distance, i.e., f/4, f/5.6, f/8, f/11, f/16, f/22 and f/32.

To look examine the bokeh qualities of the lenses, I focused them at their smallest common focus distance, which is 2 meters. The Lumix 45-200mm can focus down to 1 meter. Then I placed some backlit foliage in the background.

What we can note at once, is that the field of view is not the same. The Nikon gives a closer view of the foreground. This surprised me at once, and I made sure to check the EXIF to see that the Lumix picture was indeed taken at 200mm.

However, we can note that the focal length specification is always given at infinity focus, while in this case I am focusing closer to the minimum focus distance. I did confirm that at infinity focus, the field of view of the two lenses is the same.

To better compare the bokeh, I am providing 100% crops from the two images above (click to enlarge):

It is pretty difficult to conclude anything from this test. I think I was a bit unlucky with my test subject, it doesn't reveal any bokeh weaknesses that easily. Perhaps we can say that the 45-200mm bokeh at 200mm is a bit more "dirty". But it's hard to point out any significant weakness with any of the bokeh examples.

In the Nikkor 200mm image, it is possible to see the diaphragm blades, since it is stopped down one step. The Lumix bokeh rings, on the other hand, are round, since the lens is not stopped down at all.

The Nikkor could appear to be less affected by flare, which is natural due to it's simpler construction with a much smaller number of lens elements.

Sunday, 18 July 2010

Diffraction is a physical phenomenon. In digital photography, it is used to describe the blur which is associated with a high sensor pixel pitch, and a small aperture. This blur will potentially make your images less sharp, when you close down to very small apertures. This is still a physical phenomenon, and not a defect with the camera or the lens.

The amount of diffraction depends on the pixel pitch, and the aperture opening. The sensor pitch depends on the sensor size and the number of pixels. The smaller the sensor, or the higher the number of megapixels, the more diffraction. Also, the smaller the aperture, the higher the diffraction.

For Micro Four Thirds cameras, it is generally said that one should be careful using apertures smaller than f/8. For example, f/11 or f/16 could potentially generate diffraction.

This can be a problem with macro photography, in which you will need to close down the aperture a lot to get sufficient depth of focus. How much can you close down the aperture before the diffraction becomes a problem?

Here is a series of images taken as maximum magnification with the Panasonic Lumix Leica 45mm f/2.8 1:1 macro lens. Focus was set on the middle LEGO face eyes. The left face is 8mm to the front of the centre face, and the right face is 8mm to the rear. One LEGO unit is 8mm. Click on an image to view it larger.

f/2.8:f/4:f/5.6:f/11:f/22:
As you can see, the depth of focus increases as the aperture gets smaller. Looking at these scaled down images, it is hard to see much effect of diffraction, though.

To examine the effect of diffraction more closely, let's look at 100% views of the centre face mouth. Click on the image to view it larger.

What we see here, is that the image taken with f/22 shows some diffraction effect. It is less sharp than the other images.

Still, it is up to the user to decide what is more important: Depth of focus, or sharpness at pixel level. If it is important to have a large depth of field, I would say the image taken with f/22 is the best, despite some dullness at the 100% view. If used on the web, for example, this dullness would not matter at all, due to scaling the image down to fit a typical window. Looking at the series of images above, the latter one is the most sharp on overall, despite being less sharp when zooming in.

The conclusion here, I think, is that when using f/16 or smaller, there is some diffraction effect. However, you should not be afraid to use these apertures, if depth of focus is important. The photographer must decide what is most important.

Thursday, 15 July 2010

As a macro lens, the Leica Lumix 45mm f/2.8 is pretty ordinary. The max aperture f/2.8 is completely adequate for a macro lens, in fact, you would usually want to stop down to at least f/5.6 when taking close up pictures. Closing down for macro images is a necessity to achieve some depth of focus.

However, I think a lot of people also anticipated to use this lens as a portrait lens. Being the only prime lens available for the Micro Four Thirds format with a typical portrait focal length, there are not any alternatives at the moment. And I think some would find the max aperture of f/2.8 to be too small for portrait use. High end portrait lenses typically come with a max aperture of f/1.4, which is two stops larger than f/2.8.

Saturday, 10 July 2010

The "rolling shutter" concept is related to the shutter not reading out the exposure values at once, but rather scanning across the sensor vertically or horizontally. This implementation could be mechanical, as with the shutter curtain on the Micro Four Thirds cameras, or electronical, as when the sensor output is read during a video recording.

This is not strictly related only to digital cameras. Older film based cameras often feature a focal plane curtain shutter, which "rolls" across the film plane and exposes the film horizontally or vertically. A very famous example of this is the racing car picture taken in 1913 by Jacques Henri Lartigue using a 4x5 Speed Graphic camera.

The shutter moves relatively slowly on this camera, when compared with modern SLRs, which gives the distortion of the racing car. The distortion is especially visible in the wheels, which appear to be leaning forward. This effect was later copied by cartoonists when they wanted to give the impression of speed.

The Olympus 50mm is not optimized for Contrast Detection Autofocus (CDAF), and will autofocus slowly on MFT cameras, and not at all on the first series of Panasonic MFT cameras (G1, GH1, GF1). The Olympus has an edge when it comes to maximum aperture, one full stop faster than the Lumix Leica. On the other hand, the Lumix Leica has optical image stabilization built in.

This study looks into the bokeh (out of focus rendering) for a typical portrait setup. In the comparison, the subject, which is not a face in this case, is about one meter away from the camera. This corresponds to a headshot distance. The background foliage is about five meters from the camera. When taking a portrait under these conditions, it is important that the background is nicely blurred, and does not stand out to distract from the main subject.

Here is the full image, taken at maximum aperture with both lenses. The images were taken within less than five minutes, so the lightning is mostly similar. I used a tripod, and ISO 100 in all the images. I used the P exposure mode, and auto white balance. The camera used was Panasonic Lumix GH1.

What's more interesting in terms of bokeh, though, is to compare 100% views of various regions at the same aperture.

Here is the centre at f/2.8 (click to enlarge):The centre at f/4 (click to enlarge):The centre at f/5.6 (click to enlarge):Here's also 100% crops from the lower left corner. Since the field of view is not exactly the same for the two lenses, the crop might not be from exactly the same area.

The corner at f/2.8 (click to enlarge):The corner at f/4 (click to enlarge):The corner at f/5.6 (click to enlarge):Conclusion

Honestly, I was expecting the Olympus 50mm lens to perform best in terms of bokeh. This study, however, shows that the bokeh is somewhat smoother with the Lumix Leica 45mm. The highlight circles have harder edges with the Olympus 50mm.

However, anyone possessing the Leica Lumix 45mm f/2.8 macro are likely to be using it with a larger aperture than f/5.6. Therefore, it makes sense to examine the bokeh for larger apertures as well.

The setup is still the same: The focus distance is one meter, and the background foliage is about five meters away from the camera. This is consistent with typical portrait situations, in which you fill the head into the frame, and want the background to be blurred and non-distracting.

All the images were taken within less than one minute, and the lightning is hopefully pretty similar for all of them. I did not use any filters on the lens. The camera used was the Panasonic Lumix GH1, at ISO 100.

Here is the full image, taken with f/2.8. The image is scaled down and sharpened a bit, otherwise unchanged from the camera JPEG.

To learn more about the bokeh characteristics, let's look at 100% crops from various parts of the image. Here are 100% view crops from the centre of the image, at f/2.8, f/4 and f/5.6. Click on an image to see an enlarged view.

And crops from the upper right hand corner:

Finally, crops from the lower middle region:

Conclusion

The bokeh looks better at larger apertures. There is still some ringing around the highlights even at f/2.8. This causes some distraction, even in the downscaled view. However, keep in mind that this is a very tricky situation for any lens to render.